1. Field of the Invention
The present invention relates to an optical scanning device used in an image forming device such as a laser printer. The present invention also relates to the image forming device employed with the optical scanning device.
2. Description of Related Art
An image forming device, such as a laser printer, employs an optical scanning device. The optical scanning device has a reflecting body such as a polygonal mirror. The image forming device modulates a laser beam emitted from a laser element, such as a semiconductor laser element, based on image information. The reflecting body deflects and scans the laser beam and focuses the laser beam on the surface of the photosensitive body, thereby forming an electrostatic latent image on the photosensitive body. The electrostatic latent image is then developed into a visible image by developing agent.
The optical scanning device is generally provided with a synchronization detection element. The synchronization detection element performs synchronization detection by detecting the light scanned by the reflecting body in order to synchronize the repeatedly-executed scanning operation with the image information desired to be recorded.
In order to let the synchronization detection element attain sufficient optical-reception sensitivity and to attain an accurate synchronization detection, the light deflected by the reflecting body has to be formed into a sufficiently small-diameter beam before the light falls incident on the synchronization detection element. It is therefore preferable to make the length of the optical path from the deflection point on the polygonal mirror to the synchronization detection element substantially equal to the length of the optical path from the deflection point on the polygonal mirror to the photosensitive body.
There has been proposed a conventional optical scanning device, which has both the semiconductor laser element and the synchronization detection element on the same surface of its base plate.